This invention relates to a particular foil sail for vessels and more particularly to a rotating foil arrangement that employs a plurality of parallel elongated narrow vanes. In small sailing craft, and particularly in sailboards, as for example those illustrated in U.S. Pat. No. 3,487,800, it is common to employ a single triangular cloth sail which can be carried freely at various angles to the wind as a result of a universal joint at the base of the mast. When angled to windward and back, this rig is capable of simultaneously creating forward and upward lift, and the successful combination of these two forces has improved upon the conventional rigs as evidenced by the fact that the sailboard rig now holds the monohull speed record of over 35 knots. Efforts have been made to improve the lift performance of sails by improving rigidity, smoothness, and using high aspect ratio for better results. Thin, rigid, single high aspect ratio air foils have not been too successful because the height necessary to achieve the required sail area makes these rigid foils very difficult to control. In addition, a single foil requires some stiffening agents such as a mast to supply enough rigidity for control. It has accordingly been difficult to improve upon the present sail arrangements of a mast with synthetic cloth, highly tensioned by battens and using a wishbone boom which creates in effect a sail that is a very taut membrane and which is quite efficient.